Method for effecting an electronic drive control

ABSTRACT

The invention relates to a method for effecting an electronic drive control of a drive coil of a protection system using an electronic device which comprises a microcontroller. The aim of the invention is to increase the serviceable life of a protection system. To this end, the invention uses a randomly selected and constantly changing delay time (t x ) that occurs after a time (t 2 , t 3 ) at which the supply voltage is established on the electronic device.

BACKGROUND

The present invention relates to a method for controlling a drive coilof a contactor.

An electronic drive control for a magnetic drive is known from EuropeanPatent Application EP 0 789 378 A1.

If the control voltage of a contactor is drawn from one of the threephases, synchronization effects can ensue between the closing or openingangle of the main contacts in the load circuit and the AC controlvoltage.

This is due to the fact that a certain voltage build-up of the supplyvoltage for the electronics has to take place.

If the control voltage is switched on at voltage zero, then the supplyvoltage does not build up immediately but only at a later point in time.Around this point in time, an unwanted synchronization takes place as aresult of which one of the three switching contacts of the contactor isalways subject to higher wear. This means, that one contact has aswitch-on point at which the voltage level is approximately identical,independently of the instant of the control signal. Since the servicelife of the contactor depends on the service life of the most erodedcontact, the synchronization results in shortened service life of theoverall device.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for electronicdrive control of a drive coil of a contactor with which the service lifeof the contactor is increased.

The present invention provides a method for controlling a drive coil ofa contactor having main contacts for a load current. The method includesproviding an electronic drive control apparatus including amicrocontroller. A randomly selected constantly varying time delay isapplied in the microcontroller after a time at which a supply voltagehas built up at the electronic drive control apparatus and before a timeat which the supply voltage is measured.

Via the present invention, an irregular erosion of the switchingcontacts is prevented and, consequently, the service life of thecontactor is increased.

With reference to the drawings, embodiments of the present inventionwill be described and illustrated in greater detail.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be elaborated upon below with reference tothe drawings, in which:

FIG. 1 shows a timing diagram in accordance with the present invention;

FIG. 2 depicts a timing diagram without delay time in accordance with aprior art system;

FIG. 3 shows a schematic representation of an electronic drive controlsystem;

FIG. 4 depicts a flow chart of a first embodiment of a method forcontrolling a drive coil of a contactor; and

FIG. 5 shows a flow chart of a second embodiment of a method forcontrolling a drive coil of a contactor.

DETAILED DESCRIPTION

FIG. 1 shows a timing diagram in which the rectified supply voltage isshown in a lower graph, the supply voltage being an AC voltage.

Subsequent to switching on the supply voltage at instance t₀ which islies at the voltage zero crossing, the voltage of the electronics buildsup only after 3 to 5 ms. Subsequent to this voltage build-up, a resetsignal occurs for a microcontroller. The program is started. After thisinstant t₁, the state is detected in which the contactor is operated. Itis checked which type of control is concerned. The detection refers tothe conventional operation, programmable control operation or low-poweroperation. This input recognition takes approximately 5 ms, the end ofrecognition being denoted by t₂. If a voltage level is present, then theconventional operation is detected.

After this point in time, to prevent synchronization effects, provisionis made for a randomly determined delay time t_(x) ranging between zeroand half the period duration of the control voltage.

The supply voltage is measured only after this delay time, the point intime being denoted by t₃, it being possible for the supply voltage to beboth a DC and an AC voltage. In this connection, it is checked whichsupply voltage is concerned (AC or DC). The level of the applied voltageis ascertained at the same time.

After t₃, it is checked, moreover, whether the supply voltage lieswithin a predetermined voltage window Umin, Umax, i.e., whether thedetermined value lies in the permissible range.

These processes take approximately 12.5 ms, it being possible forinstant t₄ at which the contactor drive is activated, that is, thepickup process is initiated, to lie at any point of the sine curve ofthe supply voltage due to delay time t_(x). The time of the pickupprocess is different, depending on the contactor type. Depending on thecontactor type, the pickup takes place after 50 to 100 ms.

Switching point t₅ of the contacts is distributed at random for theother phases as well, resulting in a uniform loading of the switchingcontacts.

The unwanted synchronization effect will be explained in greater detailwith reference to FIG. 2. The broken lines show different switch-onpoints with which different voltage values can be associated. Since thevoltage for starting the microcontroller must first be built up, thereset signal lies always at the same point of the curve nearlyindependently of the switch-on time so that the switch-on times arevirtually synchronized to the same reset time.

If the control voltage is switched on, for example, at the voltage zeropoint, then the supply voltage for the electronics does not build upimmediately.

Using the explained method, unwanted synchronization effects between theclosing angle or opening angle of the main contacts in the load circuitare prevented.

To implement a timing element having a variable time which is set atrandom, a random-number generator is required. The value delivered bythe random-number generator is subsequently processed in such a mannerthat, via the subsequent processing of the value, a time from zero tomaximally half the period duration of the control voltage ensues.

A random value is obtainable in two ways.

FIG. 3 shows a schematic representation of an electronic drive controlsystem.

In a first embodiment, a value in a RAM storage location 11 in themicrocontroller is read out, the content of this cell subsequent toswitching on the voltage being undefined.

In a second embodiment, a value is obtained form a storage cell, orlocation, 1 of an EEPROM, the value being manipulated appropriately. Theold value is utilized for determining the new value. The old value isthen replaced with the new value in the EEPROM.

FIG. 4 shows the appertaining flow chart for the implementation with aRAM.

In a second embodiment, a value is obtained from a storage cell, orlocation, 1 of an EEPROM, the value being manipulated appropriately. Theold value is utilized for determining the new value. The old value isthen replaced with the new value in the EEPROM.

Subsequently, the manipulated value is written into a register 2. Then,the timer is started. When the timer reaches the value zero, then atimer underflow ensues which is forwarded to the CPU, and the program iscontinued.

FIG. 5 shows the corresponding flow chart.

Due to this additional time loop, the closing and opening angles of themain contacts with respect to the control voltage are not synchronized.

What is claimed is:
 1. A method for controlling a drive coil of acontactor having main contacts for a load current, the methodcomprising: providing an electronic drive control apparatus including amicrocontroller; and applying a randomly selected constantly varyingtime delay in the microcontroller after a time at which a supply voltagehas built up at the electronic drive control apparatus and before a timeat which the supply voltage is measured.
 2. The method as recited inclaim 1 wherein the delay time has a magnitude between zero and half aperiod duration of a control voltage of the electronic drive controlapparatus.
 3. The method as recited in claim 1 further comprisingstarting a detecting of a type of control in which the contactor isoperated and wherein the applying the time delay is performed after acompletion of the detecting the type of control.
 4. The method asrecited in claim 3 wherein the type of control is at least one of aconventional operation, a programmable control operation and a low-poweroperation.
 5. The method as recited in claim 4 wherein a time differencebetween a start of the detecting the type of control and the completionof the detecting is approximately 5 ms.
 6. The method as recited inclaim 1 further comprising checking the supply voltage for at least oneof AC and DC operation after the applying the delay time.
 7. The methodas recited in claim 1 further comprising checking, after the applyingthe delay time, whether the supply voltage lies within a predeterminedvoltage window.
 8. The method as recited in claim 1 further comprising:checking the supply voltage after the applying the delay time; andactivating the drive coil approximately 10 to 15 ms after a completionof the checking so as to initiate a pickup operation.
 9. The method asrecited in claim 8 wherein the activating is performed 12.5 ms after thecompletion of the checking.
 10. The method as recited in claim 1 furthercomprising determining the delay time using a timing element operatingas a random-number generator, the random-number generator producing avalue which is subsequently processed so as to yield a time from zero toat most half a period duration of a control voltage of the electronicdrive control apparatus.
 11. The method as recited in claim 1 furthercomprising reading from a RAM storage location of the microcontroller avalue to be associated with the delay time, a content of the storagelocation being undefined subsequent to a switching on of the supplyvoltage.
 12. The method as recited in claim 11 further comprising:manipulating the read value; then writing the manipulated value into aregister as a timer; then starting the timer so as to achieve a timerunderflow when the timer reaches a zero value; then forwarding the timerunderflow to a CPU; and then continuing a program.
 13. The method asrecited in claim 1 further comprising: reading a value from a storagelocation of an EEPROM; determining a new value from the read value; andreplacing the read value with the new value in the EEPROM.
 14. Themethod as recited in claim 1 further comprising measuring and checkingthe supply voltage.